If there are cached notification icons for a provider, then you disable social and restart, those cached items are still used, even though they are not visible. This can result in errors in the js console:
Timestamp: 23/10/2012 11:34:42 AM
Error: TypeError: navigator.mozSocial is undefined
Source File: https://s-static.ak.fbcdn.net/rsrc.php/v2/yE/r/e96h7ImncfC.js
Line: 6

Created attachment 674098[details][diff][review]
only use the toolbar cache when provider is active.
We probably want this in aurora/beta too as it may appear as though the provider is being "pinged" even when disabled.